1. Field of the Invention
The invention relates to a method and an apparatus for manufacturing a magnetic transducer having properties of changing in electrical resistance in response to an external magnetic field, a method and an apparatus for manufacturing a magnetic head having a magnetic transducer, software and system for controlling manufacturing of a magnetic transducer, and software for estimating resistance value of such a magnetic transducer, and computer system.
2. Description of the Related Art
Recently, an improvement in performance of a thin film magnetic head has been sought in accordance with an increase in a surface recording density of a hard disk drive. A composite thin film magnetic head, which has a stacked structure comprising a recording head having an inductive magnetic transducer for writing and a reproducing head having a magnetoresistive (hereinafter referred to as MR) element for reading, is widely used as the thin film magnetic head.
The MR element utilizes an MR film changing in electrical resistance in response to an external magnetic field. MR elements include an AMR element utilizing an anisotropic magnetoresistive (AMR) effect, a GMR element utilizing a giant magnetoresistive (GMR) effect, and so on. The reproducing head using the AMR element is called an AMR head or simply an MR head, and the reproducing head using the GMR element is called a GMR head. The AMR head is used as the reproducing head whose surface recording density exceeds 1 gigabit per square inch, and the GMR head is used as the reproducing head whose surface recording density exceeds 3 gigabits per square inch.
Methods of improving the performance of the reproducing head include a method in which a pattern width of the MR film, particularly, an MR height is made appropriate, and so on. The MR height refers to a length (height) of the MR element between the end thereof close to an air bearing surface and the opposite end thereof. The MR height is controlled in accordance with an amount of polishing of the air bearing surface. Incidentally, the air bearing surface refers to the surface of the thin film magnetic head facing a magnetic recording medium (a disk medium) and is sometimes called a track surface.
This type of thin film magnetic head is manufactured through the following steps as proposed in Japanese Patent Application Laid-open No. Hei 11-863, for example.
First, a large number (a large number of sets) of head cores, each of which includes a reproducing head using an MR element and a magnetic induction type recording head, and thin film structures such as dummy sensors are formed on a wafer (a substrate) made of, for example, a predetermined ceramic material by a thin film process using photolithography or the like. The dummy sensor is used for monitoring in order to control dimensions and performance of the MR element.
Then, the wafer is cut into a plurality of rectangular bars, each of which includes a plurality (a plurality of sets) of head cores and dummy sensors, by the use of a dicing saw or the like.
Then, a plurality of bars thus obtained is set on a polishing apparatus or the like, the cut surfaces thereof (the surfaces which are to be finally the air bearing surfaces) are polished, and polishing is stopped when the MR height of the MR element reaches a predetermined target dimension. The term “a predetermined target dimension” generally refers to a target value predefined as a dimension capable of delivering electromagnetic performance required for the reproducing head.
For example, Japanese Patent Application Laid-open No. Hei 2-96572 proposes a method which includes: directly measuring resistance values of a plurality of MR elements formed on the bar; calculating a mean value of the resistance values; and stopping polishing the bar when the mean value reaches a value within a predetermined range, not a method which includes controlling the timing of stopping polishing the cut surface of the bar while measuring the MR height. Incidentally, the polished bar is further cut into separate head sliders.
However, the method in which polishing is controlled until a mechanical dimension value of the MR height reaches the target value has a problem. Although the thin film magnetic head is manufactured with the intention of obtaining the MR element having predetermined electromagnetic performance, variation or an error out of predetermined tolerance is often detected when electromagnetic properties of the manufactured MR element are measured. When the electromagnetic properties of the MR elements of many thin film magnetic heads finally obtained are measured and the mean value of the electromagnetic properties is calculated, the mean value is sometimes out of predetermined tolerance. This problem is considered to arise because in forming the MR film on the wafer, a change in various conditions for photolithography or film forming or the like causes variation in a thickness or pattern width of the formed MR film according to an inter-wafer or in-wafer position.
The method, in which polishing of bars is controlled by measuring the resistance values of the bars during polishing and monitoring the mean value of the resistance values, theoretically allows the mean of the resistance values of the MR films of the bars under polishing to be within a predetermined range of numerical values. Even if the resistance value of the MR film is within tolerance, the method cannot, however, ensure that the MR height is within tolerance. Incidentally, not only the resistance value of the MR film but also the MR height is specified because too small an MR height may cause a phenomenon such as electro migration and thus cause damage to the MR film.
As described above, a problem has heretofore existed: variation in the resistance value or the dimension (MR height) of the MR element of the thin film magnetic head finally obtained occurs, and therefore the thin film magnetic head which does not fulfill required specifications is disadvantageously manufactured.
The invention is designed to overcome the foregoing problems. It is an object of the invention to provide a method and an apparatus for manufacturing a magnetic transducer and a method and an apparatus for manufacturing a magnetic head which make it possible to fulfill specifications for predetermined magnetic reproducing by reducing variation in electromagnetic properties of an MR element finally obtained and variation of the median of distribution.